This invention relates to systems for, and methods of, irradiating articles, and particularly food articles, to sterilize the articles. The invention particularly relates to systems for, and methods of, irradiating opposite sides of the articles with cumulative irradiation between first and second intensities at all positions in the articles to sterilize the articles.
It has been known for some time that drugs and medical instruments and implements have to be sterilized so that they will not cause patients to become ill from harmful bacteria when they are applied to the patients. Systems have accordingly been provided for sterilizing drugs and medical instruments and implements. The drugs and the medical instruments and implements are then stored in sterilized packages until they are ready to be used.
In recent years, it has been discovered that foods can carry harmful bacteria if they are not processed properly or, even if they are processed properly, that the foods can harbor such harmful bacteria if they are not stored properly or retained under proper environmental conditions such as controlled temperatures. Some of these harmful bacteria can even be deadly.
For example, harmful bacteria have been discovered in recent years in hamburgers sold by one of the large national hamburger chains. Such harmful bacteria caused a number of purchasers of hamburgers from stores in the chain to become sick. As a result of this incident and several other similar incidents, it is now recommended that hamburgers should be cooked to a medium state rather than a medium rare or rare state.
Similarly, harmful bacteria have been found to exist in many chickens that are sold to the public. In view of a number of incidents which have occurred, it is now recommended that all chickens be cooked so that no blood is visible in the cooked chickens.
To prevent incidents such as discussed in the previous paragraphs from occurring, various industries have now started to plan on sterilizing foods before the foods are sold to the public. This is true, for example, of hamburgers and chickens. It is also true of fruits, particularly fruits which are imported from foreign countries.
The food articles are generally irradiated from opposite sides of the articles. The cumulative amount of radiation at every position in the food articles should be at least a first magnitude to insure that all of the harmful bacteria in the articles are destroyed. The cumulative amount of radiation at every position in the articles should be less than a second magnitude to insure that beneficial bacteria in the articles have not been destroyed. The second magnitude is greater than the first magnitude. The range of the cumulative radiation in the articles between the first and second magnitudes may be considered as optimal values of radiation.
The food articles may be provided with different thicknesses. It has been found that the cumulative amount of the radiation is different for different thicknesses of the food articles. For example, flat hamburger patties weighing one-half of a pound (xc2xd lb.) have a different width or thickness in the flat plane than hamburger patties weighing a quarter of a pound (xc2xc lb.). Because of this, the cumulative amount of the radiation at various positions in the one-half pound hamburgers may be different from the cumulative amount of radiation at different positions in the one quarter pound (xc2xc lb.) hamburgers.
For a first range of article thicknesses, the amount of the cumulative irradiation in the articles has been at the optimal values. For a second range of article thicknesses greater than the thicknesses in the first range, the cumulative amount of the radiation in the articles has been found to be greater than the optimal value. For a third range of article thicknesses greater than the thicknesses in the second range, the cumulative amount of the irradiation at the different positions in the article has been found to again be at the optimal values.
As will be seen from the discussion in the previous paragraph, a problem exists when the width or thickness of the food articles is in the second range since the cumulative amount of the irradiation at the different positions in the article is greater than the optimal values. The problem is compounded because the thicknesses in the second range are between the thicknesses in the first and third ranges where the cumulative amount of irradiation at the different positions in the articles is at the optimal values.
In a preferred embodiment of the invention, opposite sides of an article are irradiated to sterilize the article. The cumulative irradiation should be above a first value, and below a second value greater than the first value, at all of the positions in the article to provide the article with desired radiation benefits. Any amount of cumulative radiation between the first and second values is considered as optimal values.
For a first range of article thicknesses, the cumulative radiation in the article is at the optimal values. For article thicknesses in a second range greater than the first range, the cumulative radiation at positions in the article is greater than the optimal values. For article thicknesses in a third range greater than the second range, the cumulative radiation at the different positions in the article is at the optimal values.
For the thicknesses in the second range, a member disposed in the radiation path weakens the radiation passing to the article, thereby reducing the cumulative radiation to an optimal value. For each thickness in the second range, a different amount of cumulative radiation above the optimal value may occur when the member is not disposed in the radiation path. The member may accordingly be provided with different thicknesses, dependent upon the amount of the cumulative radiation in the article for the different positions in the second thickness range, to reduce the cumulative radiation in the article to an optimal value. A system operative automatically positions the members properly for article thicknesses in the second range.